Frequency divider



Oct. l1, 1949.*r

K. H.`DAvls' FREQUENCY DIVIDER 2 Sheets-Sheet l Filed Dec. 19, 1946 Oct. 1 1,V 1949. K. H. DAvls FREQUENCY DIVIDER Sheets-Sheet 2 OU TPU T ourpur mm fm NF. V'

Patented Oct. 11, 1949 FREQUENCY DIVIDER Kingsbury H. Davis, Bernardsvlle, N. J., assignor toBell Telephone Laboratorios, Incorporated, New York, N. Y.,V a corporation of New York Application December 19, 1946, Serial No. 717,111

(Cl. Z50-36) 12 Claims.

This invention relates to alternating wave generators and particularly to such generators of th type known as relaxation oscillators. i

The relaxation oscillator, particularly of the multivibrator type has had many applications in frequency dividing systems. The usual arrangements have employed single or tandem operations of multivibrators to reduce a higher control frequency to some one yor more desired lower frequencies. These prior art systems have been limited to applications wherein the obtained divided frequency bears an integral relation to the original undivided control frequency. With these systems, whenever the desired frequency conversion does not present such an integral relation, the conversion must be effected through combined operations involving frequency division and frequency multiplication. Furthermore, prime number frequencies, Which'have cyclic variations numerically greater than a low hunting value are indivisible by these systems when the divided output is required to have an integral number of cyclic variations each second. This low limiting value has as a' limit the numerical stepdown ratio that may be practically realized in one stepdown operation.v

This invention makes possible the direct conversion of an alternating electromagnetic force from a higher to a lower frequency value by a ratio which may be a prime number greater than the stepdown ratio obtainable in a single stepdown operation.

The invention also makes possible frequency conversions wherein the divided output frequency bears a fractional relation to the original undivided frequency.

Electromagnetic waves having a large prime number of cyclic variations per 'second may, through the means provided by this invention, be converted to waves having fewer rcyclic variations per second and having a frequencywhich is'integrally related to the original frequency.4

The manner in which these and other desirable results are accomplished, and the attendant advantages which may be realized through the use of the invention, will be'more apparent from the following description considered in conjunction Fig. 5 shows an arrangement for securing a fractional frequency product, and;

Fig. 6 shows an embodiment of the invention in which the feedback voltage is alternately connected to the input circuits.

The invention utilizes the principle that a condenser in charging from a constant potential source through a constant resistance experience a voltage increase which follows the relation:

This is an exponential function which has its greatest slope at the start of the charging operation and which approximately maintains this slope for a small percentage of the total charging range. This substantially constant slope may be extended, to approximate a linear function, over a limited voltage range by the proper choice of the charging voltage E, and additionally the slope of the linear portion may be changed Within narrow limits by the choice of the charging voltage E. In the usual prior art multivibrator oscillator circuit, this charging voltage is maintained at a substantially constant level and the oscillator has a characteristic natural timevfor reversals. Where the oscillator is to be synchronlzed to a submultiple frequency of a wave, this characteristic natural time of reversal is so selected that it is reversed by the last of a group Kof cycles of the synchronizing wave at a, time just prior to its natural reversal time.v The interval between reversals may be the same for both sides of the multivibrator, in Which case the circuit is symmetrical and balanced, or it may be different for the two sides, in which case the circuit is unbalanced.

If a normally balanced multivibrator has its characteristic natural reversal time changed on one side only, it becomes an unbalanced unit; and experiences a change in the time required for its cyclic operation. However, if a normally balanced unit has its reversal times reciprocally changed on both sides, that is, one side increased by the same period that the complementary side is decreased, theunit becomes unbalanced; but there is no frequency change as the time required for its cyclic operation remains unchanged. Accordingly, the balance relations of a multivibrator oscillator partially disclose its operating characteristics and may be'defln'ed as a ratio of the non-conductive intervals of the respective sides of the unit. During the following description this ratio is expressed in terms of input cycles.

The present invention-employs the foregoing principles` to. control .theyoscilla'tirlg;rv characteristics of tandem operated multivibrator units. This control is effected through one or more voltages:5

that are fed back from subsequent to preceding units in the tandem array to change eith'e'rthej balance ratio or the frequency .oitoscillationofjthef controlled unit. The mutivibratorunitsthat are to be thus controlled may be constructed-anaccordanc'e With well-known principles covering the design of a unit having a specified"riaturatirne" ed value when the charging voltage is changed.

Reference Will be made to this variation in describing the operation of the circuits of Figs. 1 and 3 to 6. In the-arrangementgofFig-. 1. thevacuumtubes It and IB perform a pulse inverting, amplifying and clippingv ,functionn This stage isl helpfull but not'essentialg in the voperationdof this freddi-:lloy-v dividing system. The vacuum tubes I3 and 2li with their associated resistance and capacitance circuit components form the multivibrator' Il, which in this embodimentv operates as a variable-ratio'unit having a 's'tep'do'wnratio of 15.7' to 1. The' following stage' I2 comprises vacuum tubes 22V and 24 togetherjwith' the u'sual'multi'- vibratorY resistance an'dcap'a'citance circuit components, andoperatesatal to 1 stepdown .ratio With're'spect'to the previous/stage II.

' The plate Yor anode 2610i Vacuum-13111092.41 is. connected to the contr'o'lgrivdgof the tub 61Min.

the preceding stager I'I through the' interconnectingcircuit 3lincl`udii'g resistor 32; Whereas the multivibrator II isv a normallybalanced unit;

the multivibrator |21 is-"unbalanced in the ratioi of 61/2- to 31/2,-withthe tube 22" remaining cut'o' fori the longer period. t Because the multivibraratio. plied to only one-of its control grids3jfror'nthe plate o-r anode 36 of the preceding stagefIZ' by Way of the interconnecting circuit 38"includingv The period ofthe" t'hercoupling condenser 40; y uncontrolled'side of the multivibrator i3 is made equal to one-half of the total control period, and

the output from this stage`l3" is balanced.

Inoperation, the input wave, the. frequency of'l which is tov be reduced, and which, thoughher'e shown as the pulses'42,"'may be pulses or cyclic variations, is applied through the couplngunits.

44 to the controlY grids 4'6 .andY 48'` of the-.pulse inverter stage Ill. y The. 'tubes EIL-and'. IIS .aref so biased that they'are normallyin a saturated plate current condition, and the positive pertion.

of the input pulse causes little or noreaction at j The '.negativeportion of the pulse/gives rise to asharp positive.

the plates or anodesv 50, .52.

plate voltage increasethat is available as the positive pulses. 54 for synchronizing the fretor I2 isunbalanced,"the-positive and negative 5"@ portionsof itsfoutput Wave ar'eunequal. In'ordery to secure a symmetrical output wave, thefbalanced Ymultivibratorv I3 is operated ata 1 lto l Control synchronizing pulses are sup-v quency division circuit II in the usual Wellknown manner. Assume, for reference purposes, that thetubes 2l),y \22 aref-conducting current and tubes I8, ..24 ar'cut off .-As: thevv multivibrator I3 acts only as a 1 to 1 ratio unit to bal- VV.ance the positive and negative portions of the output. waves, its detailed cyclic operation is not believed-'necessary in this description. If the -tubev24j is nan-conductive, the positive voltage orr-itsplate-.ZS.is-the same as the charging volt- .ag-e -to whiclfrJtheplate-grid coupling condenser 56, is returned by way of the grid resistor 58. This A voltagis" inca'tdin Fig. 2 by the horizontal linei.' .Under these circumstances, the multivibrator II is balanced; and the condensers 5t and 62111 its timing-circuits ieach charge along the exponential curve-6.4 (Fig. 2). If not limited by grid current,' these charges would approach.

the chargingr voltage `V6p in asymptotic manner-,1 as rindicatedqb'yfthe. dotted portion of the ating cycles andis" changing kfrom a cut-off'to a conducting state with the.l usual drop in voltage at its plate or anodef'l.. Multivibrator I2 is so proportioned 'that it's/ tjibe a22 has.v been conducting'V during" these- 31/2 cycles of the preceding stage II.v VB'y the usualfnrmal' multivibrator action. this tube Ztlis'novv'forced to cutoi by the'start'ovf'. conduction in its complementary tube 24,M and a sharp`d'rdpmoccursl inthe voltage level atA the'anode'26. .A't this instantthe charging ff vofltas'ge'tol theedenser.' 56v is vloweredfrom its previous positive voltagey value .60 (Fig. 2) to Sle 1Wer`1evT`6`s (Fig. '2);tf1e'e'Xact Value Of WhiCh'iS" deteini'ed'by4 the voltage potential at the' plate 'ZB'of theftubeff andthe value chosen for the" res"`istor"'32l' 4`Under.these changed circumstances, the condenser'm charges .along the exponential curve'f'llkWhc'l'i if ndtVV limited by grid' current vlfiiilt""beclie'V asymptotic to the lowered." vciltage"'level4 '68'.y Yvvl'er'ea's the condenser continues "to" charge along'its original curve S4. In this described,v tested embodiment'. the chargingvoltag'e Wasdwei'wfro'ni aboutl 200 volts to approximately-35"volts; which change Was suiil'- cientto increasethecut-oi' period of the tube 20 .byS an interval equivalent td "one complete input cycle. 'Under' 'these'j revised". conditions, the tub'e20 is'cut off for-'8%. cycles ofthe input frequencygtubem/Iji'sicut o'lfor' 7.1/21 input cycles, and the multivibrator operates ata stepdown ratio of 1'64t`o` 1" with respect"tot.they input. cycles. This condition.' continues fontheiconduction period of` tl'ietub'ej2, vlliiclfin.A thisf tested embodiment was for th'ef interval duringl which `the preceding stage IjI/.perfrmedl/z' cyclic oper-ations,l andthe input` frequency .performed 1'0..f11/2v cyclic variations. From' the.'V foregoing itwill beob'served that the multivibrator I2. vexperiencoz-:ld` one complete cycle of A.operation while the. input-circuit of the tubes I4, I Il were receiving lg'ljinputcycles of the origina-lwave-42. Infthetested embodiment this input frequency was v9420 cyclesper second and the desired reduced4 frequency was 60 cycles per second.A As previously.;stated;l the output from the multivibrator I2 is unbalanced in the ratio of 6142 toHSl/gvthereforefthemultivibrator I3 is synchronized byipulses from onlyanode 36 of the tu-be,22 tosecure a:lmflariced:.eutputzV The uncontrolled side of this unit I3 has-the values ofits capacitance 12 andresistancewlll so; proportioned that its vnaturaloscillating periodis equivalent to one-half of the period required forone complete cycle of the preceding stage |2.'- f f In the frequency dividing system-of Fig. 3, three multivibrator units areutilized to provide increased stepdown-ratios. .For the sake 'of simplicity, this and the following figures ofthe drawing are in block schematic form, and .do not indi cate the usual multivibrator Icircuit components as they are not necessary for a complete understanding of the operation of the invention. Though notV indicated, each multivibratorv -includes suitable timing circuits interconnecting the anodes and grid circuits ofthe opposed sides in the usual manner." Also; forsimplicity the operation of each of the circuitsof Figs. 3,' 4 and 6 will be explained on the basis that they are functioning at a stepdown ratio of v67 to 1.f This ratio is selected as a convenient one for explanatory purposes, and does not represent the maximum stepdown capabilities of such systems, since this is a matter thatis controlledby the usual limitations experienced in multivibrator design and operation. Y f- In its general operation, the circuit 'of Fig. 8 resembles the circuit of Fig. 1, notwithstanding the physical differences in the voltage feedback circuit. In this embodiment it'will be noted that the coupling paths between-units are' crossed, that is, the plate of the'bottom tube is coupled to the control grid of the top'tube of the following unit. This particular configuration' has no operating significance, but is merely a convention that is here adopted to aid in the explanation of the circuit operation, since all top tubesmay be considered as conducting elements at the start of the reference period. l f" l In designing such a stepdown system, the first consideration is to select the normal operating ratios and balance conditions'for the: individual units. One method by whichthis selection may be made is illustrated inthe followingillustrative calculation for a ratio of l6'7 to v1. 'By'inspectiom the ratios 3, 4 and 5 form a close approximation of the desired result. Selecting' as the stepdown factor for the middle unit 80v and dividing 67 by this figure gives'a result of :132/5. This -unit80 may operate with an unbalance ratio of 2 to 3 if the unit is to be controlled 'Orione-side only. Because push-pull synchronization'is to be employed, this may be changed-to a balanced ratio of 21/2 to 21/2 without aftec'tinglthe circuitv opera# tion. Selecting the stepdown ratio fof`4 for the unit 82, and dividing the aboveobtained '13 therei by, a quotient of 3% is obtained, which indicates that the unit 82 should operate ata ratio of 4 to '1 with unbalanced periods of I 'and 3 if it is to; be operated with synchronizing lpulses onfonly one' control grid; or with periods fof v11/2 and 2l/2 if push-pull control is used, as shown.A From the foregoing, it is determined that-the system will comprise three lmultivibrator vstages 80, 82,v 84; the i-lrst of which may be a variable' ratio' unit operating at a stepdown ratio of 3 to 1 for a'portion of the time, and at a ratio of 4 to 1 for the remainder of the time. If, as in this case, the unit 88 is to operate at an odd ratio,l the unit may be balanced with non-conduction periods of l1'1/2 on each side until the voltage feedbackoccurs, at which time the controlled side will -be increased to a 21/2 period. Ii the unit-would normallyoperate at an even ratio of stepdownythe sides-may' normally be unbalanced, say 21/2 to'l'l/z'f'and'become shifted to a balanced condition'k of 2% input lcycles for each side.

The second unit may have a ratio of 5 with balanced conducting periods, and the last unit 82 may have a ratio of 4 with conduction periods of 11/2 and 21/2, for push-pull control. These values are shown parenthetically in the block schematic diagrams. To effectuate the voltage feedback, the plate or anode 94 of the vacuum tube 86 is coupled to the control grid89 of the vacuum tube 88, of the rst unit 84, through the conduction path comprising the conductor 98 and resistor 92. All of the multivibrator vunits may be designed in accordance with the usual principles Well known in this art,

and preferably with the control grid circuits returned to the same positive voltage level as is used for the plate voltage supply. The magnitude of the feedback resistor 92 is so selected that when saturation current iiows in the platecathode path of the vacuum tube 86 and the positive voltage potential at the plate 94 is lowered to its low limit, the charging voltage for the plate-grid coupling condenser (not shown) associated with the control grid 89 of the vacuum tube 88 is lowered from the level 60 to the level 88 (Fig. 2); and this change is sufficient to lengthen the non-conductive period of the controlled tube 88 by an interval equal to the desired number of input cycles. In this example, the desired interval is equivalent to one cycle of the input frequency.

The operating cycle of this Fig. 3 system may be visualized as follows. At the start of the reference period, tubes 98, |00 and |02 are conducting, and the complementary tubes 88, `81 and 88 are cut off. Unit 84 functions at a 3 to 1 stepdown ratio for 37% input cycles during which interval the unit 88 completes five reversals, or 21/2 cycles. At the end of this period, unit 82 reverses its conduction state since its tube 86 has a cut-off period that is equal to 21/2 cycles of the unit 80. The consequent drop in the level of the positive voltage at the anode 94 is fed back through the conductive path 90, 92 to the control grid -89 of tube 88 which has just started a conductive period. This lowered charging voltage has no effect on the conductive period of this tube, however, it extends the next cut-off period from its previous interval equivalent to 11/2 input cycles to a new interval which is equivalent to 21/2l input cycles. As there has been no change in' the circuit of the tube 98, the multivibrator 84l operates at a 4 to 1 stepdown ratio, with the tube 98 being cut off for 11/2 cycles, and the complementary tube 88 being cut off for 21/2 cycles.

. The multivibrator 82 has now shifted to the condition of cutoff for tube |02, where it will remain for l11/2 cycles of the preceding unit 80. After 1%/2 cycles of unit 80, during which time the tube 88 has experienced seven cut-off periods, and the multivibrator unit 84 has operated at a 4 to 1 stepdown ratio for 29% input cycles, the tube |02 againstartsconduction. Tube 86 is again cut off, with an attendant positive voltage increase at its anode 94, and the control grid 89 of vacuum tube 88 is' again returned to its original positive charging voltage level 68 (Fig. 2), to complete the cycle. During this described interval 61 cycles of the input wave have been impressed on the input unit`84.

` `In order to realize optimum operating margins inthe above-described arrangement, it is preferablel that the change in the control voltage occur at,vor near, the start of a conduction period of thefcontrolled tube. When this procedure is followedpit is apparentthat the arrangement of Eig; 3"=isrnot limited tofthefsnglt:intermediate unit-28d; as shown,z-butas many units maybe addedl as will permit th'eassembly to .completevts reversal and feedback. thei'loweredi' voltage to the controlled tube 1 before thattube becomes .cut' 01T. In. Fig. 4v thereisiindicated' van alternative arrangement which eliminates any delay" attendant upon serially reversing several intermediate units. l nthisl arrangement'-the variable-ratio multivibratorunit l/I 11S-fis control-led from, thenext adjacent unit IBS, which is'linl turn controllediby afsu-bseq-uent v.unit il. Whereas the'frst unit 1106 s-changed in-its stepdown ratio by-the feedback voltage,- the second-unit |08 maintains itsfstlepratio lou-t is-changed'yin its bala-nce arrangement-by ,the voitagecon-trolfrom the subsequent stage-Hilf. It desirable, additional multivibrator units-maybe addedto control the balance of'i'ihe` preceding bal-ance controlling uni-t Without introdancing additional vdelayvin the ratio-changing control between the firstv twounitsv 10E-and .108e This. ,latter-arrangement is indicated by the-'unit ||-2 and -its connections as-shown in -dottedlines irl-'Fiat-y VThe stepdown ratios-,and'balance relations of the. individual multivibrator units are chosen-'in thesame. manner.-described for the arrangement of: Figl-B.- Elorexample, for a 67 to 1' stepdown ratjiQ, -.the uni-t. M!! would have a ratio of v-e-w-ith an unbalance of 2 to 3, since in this-arrangement itispreferably operated-.With con-trolv pulses-on only one gridl I4.. rIhe ratiofcontrollingrunit-||18; although now in an intermediateI physical position,. continues tti-operate at-a 4 to 1 stepdown ratio. diih'ereas,v in the arrangement `of-l1"ig-..-3 the correspondingunit t2 hada fiXed-unbal-ance ofv 1% to unit. |68- now operates-at this unbalance for threeths of acycle of the-succeed ing unit, and is' then changed toanunbalance ot 2% toll/2 for the remainder of its cycle. As previously described, the variable ratiounit-|06 operatesy at a3 to ,1 ratio for a portion of the.tme and at a. 4 to --1 Aratio'for-tlie remainder ofv the complete cycle'of operations. In thepreviously described arrangement, the-'controlled tube 88 added the. same number of extra input-cycles eachf time thevoltage was lowered at -theanode S11-fot the controlling ktube 35..- In -the embodiment-ot Fig. 4,.'it should be-notedthat the controlling tube l'l'has the lowered anode Voltage for variously 1% or 2-.1/2..cyclesof the variable-ratio unit |06.'- Notwithstandingvthis difference, the same-.number of entra input cyclesr are added during the complete-stepd'own cycle, so that the overall-eiect isa 67, to 1 reduction inthe input. frequency.

-Thefs'eq'uence .of .reversals may be visualized f rom the following, if' itl is assumed that-the.cycle of operationisstarted justT as each ofthe upper ub,esr,|"|8,` |2`' |22-` 'starts its. conductive. period. Initially, the multivibrator |96 reverses. foreach- 1f1/2 cycles of input frequency.- After 271/2 suf-:hre-` versals the succeeding'unit |08 reverses so .that the tube ,l l@ conducts, and the'lowered. voltage. at. its plate |24 is vfed. back through ther con-- (,iucti've.path13|),y |32 tothe controldgrid |^-2| as the` tube f L2@ starts its conductive period. This. condition maintainsv for-ll/zcycles of the. unitillt# duri-ng which time the .tube- |28 isfcutfol once, and adds one input cycle byoperating .ata4;- tor l instead of a.3 to. 1t-stepdown ratio-...- Atfthe end-'of thiszl-'period-the `rnultivibrator unit |08ffre-f, ver-tato its originalcondition.- This process-ism@- peatedthree times,- during vwhich time theunitd 0.@

completesninecyclesjat a 3,130 1. stepdownnate'and'i` Withixincreasedpotentialf.atiits'iplate or anode |34'. Bx way Iofrtheficondnctive;paths comprising. conduetms ands VEE'382sr1d.resistors |40- and |42, thesewoltageachanges arci-applied. toz the control unit= :tUBe-'issutablyzdesignedtoi: balanced'v operatiomfw-hen the multi-vibrators conventional: grid condenser-resistors (not shown.)- are` returned to ccf-rmlwoltagei-'ilz'otential'sz 'The-'values of resistors .IAll'axxdp-H-V are-fsw selectedthat the; cutoi period of'f-:theirf-,associated tube'- I IEr-fcr :|,2.0fisf extended by oneseyple of.; tl'ie-fu-niit-fM16: when .the-Voltage :at the anodevv +31 orf 341 is lowei-*ecllto` its-.minimum value bra-plate' current conduction.. These revised voltagewconditionsreverse .the unbalance relation Within the multivibrator unit |108r soV that the. tube |f|6 now;-'condi-iota..` 'lowered Voltage. `at its plate'ycranode;|5241ffomWg-.cyclesof the first unit |106; --Durmg-,thisftime,g.the tube |28-'s cut off twice and adds one cycle of the input frequency duringeacmcutfoi periodA This condition persists yfor. `two .completet cycles-.of the unit |08, af-.terwhich-time the tube-|20- ini `becoming conductive -deliversanegntivexpulse-through the coupling-` condenser .|48f --to thev grid M4 of the saturatedztube-I. lnknownrmanner, this negative pulse-is--inverted and :delivered through the conventional. multivibrator plate-control grid coupling (-not-,shc-wn) ,to. start conduction in the upper-tube 112% of ythe balance controlling stage |40..- Th-is completes-the operating. cycle during which 67. .cycles ofthe-inputwavehave been applied to the control grids |26-, |50- of the vari-ablratio-unit- |06.-

-Ilhe ,above-described.'-arrangement may have, iii-desired; additional-:dividing stages as indicatedbythe-dotted -li-ne un-it. |-|2. As inthe case of thebalance-controllingsunitftl-, the added' stages maybe-controlled ,bfy-vpulsesr-on only one control gridandtbe. unbalanced-by whole number ratios. If. rd'esiredwa, vbalai-iced.--unity-Lr-atio Aun-it may be operatedfrom` the-last stage-tofprov-ide an output wave havingeciua-lfperiod` positive and negativev portions.. l

, |lll-1e.arrangement,indicated-in Fig. 5V illustrates one., methodbt-employingthe princi-ples of this invention-.to securej-a-truefractionalreduction in frequency -his-arrangementfemploys one fixed unbalance'stagejz and-two variable-ratioy stages- I 5,4 anda-.fl 56",. withthedesiredoutput being taken froniathe plateecathodegcircu-its of the first unit 51; -.circuit`,of;Efig...-5 isA designed for a stepdown ratloof- 3419739 :and-

eiect employs twosystemsv one .comprising .the units |52 and |55 which coopenatiyelyfeiect Aa,.-2.91to 1. stepdown ratio -ira-the previously v. ztescr-ibedmanner. The second nor-tior-i--g-oii .the .system-- comprises the unit t5# and thegoombined-eiect-ofthe two units |52, |56.- .Inthe-manner-,previously described, the nrst unit-operates at-a 3 to lastepdown ratio for 19/29 at-the' ,complete .cycle-fand ati a It to 1- ratio for lil/2a afl-titercycle.--l 4 In---each-.otf the-foregoing examples, the ratiochanging-voltage ffeedbacleconnection has been xedfnelationfito:one-'ofthe control grid circuits ot-.a-.eprecedmgfmstage vIIliis; is 'not an essential arrangement,.asisrshown'by'the circuit ofvl Fig. 6, which-illustratesoneamethodof obtaining the desired-requeney reduc-tion. :by alternately apply-- three cycles at-a 451.130 1-stepdownrate-.- Ait ,about '5 met-meizfedbaclvoltvbeezltozdne .and then the 9 other control grid of the variable-ratio multivibrator unit |58. In' the arrangement of Fig. 6, the multivibrator units |58, 60, |62 are conventionally designed units with normal balanced or unbalanced conditions as may be desired. The ratio and balance characteristics may be selected in accordance with the previously described method. Assuming a 6'7 to 1 stepdown ratio to be desired, the lastl unit |62 might preferably operate at a to 1 ratio with balanced cut-oit periods. The preceding unit |60 might operate at a 4 to 1 ratio, using cut-oir periods of 11/2 and 21/2 cycles of the preceding stage |58 which necessarily then must operate at a 3 to 1 and a 4 to 1 rate.

The gating circuit |64, shown only in simplified schematic form, serves as arelay to eiect the switching of the control voltage from one control grid circuit to the' other control grid circuit of the unit |58. The plate resistors |66, |68 are so chosen that, for saturated plate-cathode current conditions in the Ytubes |10, |12, the voltage potentials available at the points |14, |16 are the same as the potential at the plate or anode |19 during the conduction interval of the tube |80. Resistors |61, |69 are provided in the conductive paths connecting the voltage points |14, |16 to the control grid elements 208, 2|0 in accordance with the previously explained principle. The same positive plate voltage supply may be used for the gate tubes |10, |12 as is used for the multivibratorunits |58, |60, |62. Avoltage dividing network, comprising resistors |-8| to |86 inclusive, is provided in the control grid circuits of the gating tubes |10, |12. The midpoint |81 of this network is connected to the plate or anode |80 of the multivibrator tube |90 by the conductive path |92. The symmetrically located intermediate points |94, |96 are respectively connected by way of the conductive paths |98 to the plates or anodes 200 and 202 of tubes 206 and 2M. Suitable grid voltage sources, designated Ea are provided to cause the tubes |10, |12 to be non-conductive at all times except when the combined voltage potentials at the anodek |88 and either one of the anodes 200, 202 are at their maximum values. In this manner, the tubes |10, |12 never conduct current simultaneously, since the anodes 200, 202 are never at maximum plate potential at the same time.

The operation of this circuit may best be visualized if, as a reference time, it is assumed that the upper tubes |90, 204, 206 have just started their conductive cycles, and the non-conductive period of each half of each multivibrator unit is as shown parenthetically at the upper and lower left corners of the units |58, |60, |62 on the drawing. Because tube |90 is conductive, the voltage potential at its anode |88 isV low, both of the gating tubes |19, |12 are non-conductive, and the full positive plate voltage potential is available at the voltage points |14, |16. Under these circumstances, the rst unit |58 operates as a balanced 3 to l unit for 21/2 cycles, corresponding to "l1/2 cycles of the input wave; then the multivibrator unit |60 reverses its operation, and the voltage potential at the anode |88 rises to its maximum value. At this same time, the unit |62 `is conductive in its upper tube 206, with lowered potential at its anode 202, and is cut off in its lower tube 2|4, with full positive yplate `voltage at the anode 200. These voltage relations condition the gate tube |10 for current conduction which results in lowered voltage potential at the voltage point 'i 14. As explained in the previously described' cases, the resistor |61'together with the usual gridcharging resistor (not shown) in the circuit ofthe control 'grid 208 form a voltage dividing network. Acting through this network, the lowered potential at the voltage point |14 vchanges the charging voltage in this grid circuit a'nd increases the cut-off yperiod of the tube 204 from ll/g to 21/2 cycles of the input wave. The lowered voltage continues for 6% cycles of the' input wave, during which interval the unit |58 completes 11/2 cyclesv` of operation; after which the multivibrator unit |60 again reverses 'to' its'original condition, current conduction is interrupted in the gate Atube |10, and the multivibrator unit '58v again reverts to a balanced 3 to 1 stepdown'ratio unit. This series of operations is repeated for a total of 21/2 -cycles of the unit `1|60,'corresponding to 351/2 cycles of the inputfrequency'wave, at which time the multivibrator unit 62 reverses its operation so that the voltage potential at vthe anode 202, and at the `point |96 on the voltage dividing network, are at their maximum values. At this same timegthe potential at the 'anode |88 is at maximum, as the tube is cut off, and saturation current flows inl the plate circuit of the gate tube |12 tolower the voltage at the voltage point |16 and at the control grid 2|0'` of the tube 2|2. This tube 2|2 has just started a conductive period, and will experience only one cutoi period in the next 11/2 cycles, during which interval it can add an additional input cycle. Then, the multivibrator unit |60 again reverses its operation, and the 'gate tube |12 is cut off byf theY lowered voltage potential at the anode |88.l` This cyclei of operation continues for 2% cycles ofunit lyduring which time the input unit |58 has had 311/2 cycles of the input wave applied to its control grids `208, 2|0. Throughoutv this entire operation, the multivibrator unit |62 has performed o'ne complete operating cycle, while 67 cycles of the input frequency have been impressedy on the input unit |58.

Although-the invention has been described in connection with frequency division systems, it is apparent that the field-of its application is not so conned This disclosure will suggest to others skilled in the lart equivalent means for practicing the invention.

`What is claimed is:

1.An alternating' wave generator comprising aA plurality of' periodic devices, each of said devices comprising an oscillator having input and output vconnections andI a natural free-running period of oscillation, a conductive path including a series capacitive impedance interconnecting at least on'eoutput connection of a preceding oscillator and one 'input connection of the succeeding oscillatonand means responsive to the operation of said succeeding oscillator for changing the natural free-running period of oscillation of said preceding oscillator.

2. An alternating Wave generator according to claim 1 in which the means Vresponsive to the operation f said succeedingoscillator comprises a'A vdirect-currentfcoriductive circuit including a series connected resistor unit interconnecting an output connection o'f said succeeding oscillator and an input connection of said preceding oscillator. i I

l 3. lAn Aalternating Wave generator comprising a plurality of -multivibrator oscillators, each of said oscillatorshavingplate-cathode and control gridatho'degcircuits, and each s ide of each oscillator having :a natural ratio between its free-running a4-sami conductive Aand 'non-comluctive intervals., rcapaci- ,tivev elements connecting .the plate-cathode circuits vof a iirst oscillator: unitftofthezcontrol vgridcathode circuits of a ysecond oscillator unit', at least one capacitive element-'interconnecting at least vone Vplate-cathode. cincuitv l` of said second oscillator unittoat least*one-scontrolfgrid-cathode circuit :of afthird oscillatorunit, means responsive to the oscillations of :said :thi-rd` oscillator unit for changing the natural ratios between vthe said free-running'iconductive and non-conductive intervals 'of said secon'xif .oscillator"unit,; and means responsive tothe oscillations ioffsaid-v second oscll lat'ornnitorichangingthematural ratios between the l*freerunning:comluctive and :non-conductive intervals of :said rs't ns'ciflflator'funlt.

4. An alternating wave :generator in accordance ywith claim-Bun which-ithameansi for `changing the'natural ratios betweenftheffree-running conductive Hand non-conductivefritervais of isaid second oscillator is; arpluralityiof; conductive paths each lincluding fa 1 ser-iesiimpedance :element connecting each plate-,cathode `:circuit of fsaid third oscillator unit' to-foneztof.- the vcontrol kgrid-cathode circuits of saidsecond oscillator'unit, and. said means :responsivef to the oscillations of f'said'second oscillator .unit .for f :changingme :natural ratios between the freez-running. conductive and non-conductive intervals'of Asaidjfirst .oscillator unit comprises v :a :directcurrent :conductive 4path including -av .series rimpedancefelement connecting theplate-cathode:.circuitpzof one side of said second .oscillator unit rztoone; control grid-cathode circuit oi Lsaid'irslosclllator'unit..

5. An alternating fwavevfgenerator "comprising at least two :tandem-connected. multivibrator oscillators, .eachincluding a -pair of vacuum v.tubes each having :a `plate',fa :cathode andiacontrol grid, plate-cathode and control :grid-cathode circuits for each vacuum tube, a.capacitive-elementcon nected vbetweenl the 7 plate-cathode r circuit Yof Yeach vacuum .tube andthe-control grid-cathode circuit of the other tube, :at least/vone-'conductive-path containing .a series :'-connecteclf '.capacitance 'connecting .the plate-cathode:circuit' of -a -vacuum tube in one-'of the tandem-connected oscillators to the .control :grid-cathode lcircuit. of 'one of 'the vacuum tubes .inrthe :next :succeeding oscillator unit, and a direct-current conductiveacincuitzcontaining a series resistor connecting Lonez'of'zthe plate-cathode circuits of.: saidnextfsucceeding. ,oscillator unit to one foffthe' :control vgrid'- cathode circuits'of said-precedingoseillator'nnit.

6. In a frequency f dividing #system i :comprising a plurality of ^multivibrater oscillator units in tandem connection, '.eachof s said 1 units having a natural free-running "frequency vof :oscillations and comprising f plate-cathode; and :control gridcathode circuits, i inputz-mean's '.,connected yto the controlgri-d-cati-iode cincuitsziof 'therrst of A'said tandem-connected unitsnand output-means connected to the plate-cathode cincuitsscff one-of the succeedingl connectednmits; conductivexpathsrfinclucling serially-.connected impedance elements connecting .the plate-,cathode :circuits of. each preceding yoscillator unnitv to =.the.1-corrtrol gridcathode :circuits-:sof each sueoeedingzconnected oscillator unit, 'and .direct-,current f .conductive means Vresponsive :to f-alternationsinone .of said succeeding oscillator units for controlling the-fre- ;quency .or oscillation. rofl-:said first-connected unit.

f7. dA :frequency fdividingcsysl'em in :accordance with ic-lai-m -6, the. ,said means .Y for. controlling :the frequency of oscillation -.of said v:inst-connected unit comprising aldirect-currentlconductive.path

including .a serially-connected 4,impedance ele` ment connecting Aone control grid-.cathodecircuitoff-said first-connected:oscillatorunit to one plate-cathode y circuit-:of a non-adj acent succeed ing connected oscillator unit.r

-8. Inla frequencydividingfsystem for the productionof an output-wave Whose cyclicl variations bear-afractional ratiomelation :to .the cyclic variations-'of the input waveg/said `system comprisingat-least initial, intermediate and other multivibrator oscillatory :unitsv yirrtandern connection, eac-h oscillator. having -anatural free-running frequency of oscillatiomi-,eachfsuch unit comprising two plate-cathode: andtwofcontrol grid-.cathode circuits, one of said multivibrator units having input terminals connectedv tofs-its control gridcathode-,circuits for theintroduction of `the wave the frequencyof which .is-,toebe divided, and one of the Said-runitsfhaving .output terminals connected `to its Aplate.-ca-thode circuits for -the deflivery ,of the-fractional ratio .output wave, conduc-tive paths including'sserially-connected impedance e. elements i. connecting "the plate-.cathode circuit-stof leach A,precedingaosclllator unit to the control grid-cathode rcircuits of each succeedingly-v-arrangfed oscillator unit, means `responsive to the oscillations insaid succeedingly arranged multivibrator oscillator -unitsffor changing the frequency -ofV oscillation ,off/said --intermediately arrangedoscillatorunittirom its natural value toa `different value, and means responsive to the oscillationsl in fsaidfsucceedingly 4arranged multivibrator Aloscillator l:unit for changing .the freerunning 'frequency of Aoscillation-- of `the said initially arranged-oscillator unit from itsnatural toadiflerentvalue. l

.-9. ,A .frequency ydividing systemin accordance with, claim-Slvvhereinvsaid,meansffor changing the frequency l of l oscillation of` the `intermediate oscill-ator`y un-t comprises .a-direct-current conductive path including a serially-connected impedance-.connecting-one plate-cathodef-circuit of said succeedinglyfarrangedoscillator-unitto one control grid-cathode cir-cuitfof saidintermediate oscillatork uniti .fand said v-means Afor' `changing the frequencyof: oscillation -of -fsaidY initially arranged oscillatorv uni-t 4comprises :a conductive path including-'a serially-connected impedanceV connecting a :control .grid-cathode circuit of said initial oscillator unit to the other plate-cathode circuit of ,said-succeedingly: arranged oscillator unit.

v10.111 airequencyv dividing-system employing an alternating -wave generator comprising at least'three multivibrator :oscillator units in tandem connection, caChasuChs unit havingv a natural oscillatory frequenta# and a" natural balance ratio andA comprisingiplate-cathode and control gridcathodecircuits, thef-rstfone of said 'oscillator units having -lnput -terminals connected to its control grid-cathode'circuits for connection Vto the ,source :ofthefwave thelfrequency.` of which is to be-divided, outputfterminals connected to the plate-cathode circuitsv of yone of said oscillator unitsftheplate-cathode circuits-of each preceding-.unit being capacitivelyfcoupledto the controlcgrid-cathode circuits ofthe nextr succeeding unit., means-responsive tothe oscillations of one of. said Aoscillator unitsl for ychanging the frequency of oscillation of-.the said rst one of said units,Y and means responsive to the oscillations ofthe third ofsaidoscillators for-alternately reversingthe-balance ratio of the second oscillator unit.

1.1. A .frequency dividing system which comprisesa ,pair vof .multivibrator oscillator units in tandem connection, each of said oscillator units having a natural free-running frequency of oscillation, and each one comprising plate-cathode and control grid-cathode circuits, input means connected to the control grid-cathode circuits of the first of said tandem connected units and output means connected to the plate-cathode circuits of the succeedingly connected unit, an impedance element interconnecting each platecathode circuit of said first unit to a respective one of the control grid-cathode circuits of the succeeding unit, and a resistive connection between one plate-cathode circuit of said succeeding unit and a control grid-cathode circuit of said first unit whereby the frequency of oscillation of said first unit is decreased during intervals when said succeeding unit is conducting current in its plate-cathode circuit connected to said resistive connection.

12. A frequency dividing system which comprises a first and a second multivibrator oscillator unit in tandem connection, each of said units comprising a pair of electron discharge circuit elements each of which comprises a plate electrode, a cathode electrode and a control gridelectrode, said plate electrodes being resistively connected to the positive terminal of a potential source, said cathode electrodes being connected to the negative terminal of said source, a serially connected capacitor-resistor circuit connected between the plate electrode of each of said elements and a source of positive potential, the control grid-electrode of each of said elements being attached to the junction of the capacitor-resistor connected to the plate electrode of its conjugate element, the plate electrodes of said rst unit being connected to a respective one of said control grid-electrodes of said second unit, input terminal means connected to said first oscillator unit for supplying to said unit a train of Waves the frequency of which is to be divided, output terminal means connected to said second unit for the delivery of said divided frequency, and a direct-current conductive impedance element connected at its one end to a plate electrode of said second unit and connected at its other end to a junction point of one of said serially connected capacitor-resistor combinations, whereby said impedance element and said resistor form a Voltage dividing circuit to which one control gridelectrode of said rst unit is connected at an intermediate point.

KINGSBURY H. DAVIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,407,320 Miller Sept. 10, 1946 2,410,156 Flory Oct. 29, 1946 2,416,095 Gulden Feb. 18, 1947 OTHER REFERENCES Grosdoi, Electronic Counters, RCA Review, September 1946, vol. 7, No. 3, pp. 438-447. 

